Unusual Initial Presentation of Primary Lung Adenocarcinoma as a Metastatic Sigmoid Colon Lesion: A Rare Case Report

Abstract

Metastatic spread of primary lung adenocarcinoma to the colon is rare, with initial presentation as a colonic lesion being exceptionally uncommon. Differentiating primary colorectal adenocarcinoma from metastatic pulmonary adenocarcinoma poses a diagnostic challenge due to overlapping clinical and histopathological features. We describe the case of a 60-year-old man who presented with nonspecific abdominal symptoms and was found to have a sigmoid colon mass on colonoscopic evaluation. Histopathological analysis revealed adenocarcinoma, and immunohistochemical profiling supported a pulmonary origin. Subsequent thoracic imaging identified a spiculated lung mass, which on biopsy confirmed primary lung adenocarcinoma with metastatic involvement of the colon.